The invention relates to managing storage of individually accessible data units. A database system can store individually accessible unit of data or “records” in any of a variety of formats. Each record may correspond to a logical entity such as a credit card transaction and typically has an associated primary key used to uniquely identify the record. The record can include multiple values associated with respective fields of a record format. The records can be stored within one or more files (e.g., flat files or structured data files such as XML files). In compressed database systems individual records or values within records may be compressed when stored and decompressed when accessed to reduce the storage requirements of the system.